1. Field of the Invention
The present invention relates to data transmission. More specifically, the present invention relates to asymmetrical data transmission over simplex and duplex channels.
2. Background of the Invention
Cellular telephones are tremendously popular. It is estimated that at the end of 2007 the total worldwide subscriber rate reached 3.3 billion. Close to 80% of the world's population enjoys mobile telephone coverage, a figure that will only increase. As cellular telephones gain popularity, their functionality has increased also. Standard service includes voice calling, caller ID, call waiting, and voice mail. Service providers also offer text messaging, push mail, navigation, and even a high-speed internet connection directly to the telephone through the use of protocols such as those included in High Speed Packet Access (HSPA).
HSPA is a collection of wireless protocols that improve upon the performance of existing Universal Mobile Telecommunications System (UMTS) protocols. High-Speed Downlink Packet Access (HSDPA), a standard within HSPA, increases data packet transfer performance by using improved modulation schemes. These improved schemes better utilize existing radio bandwidth provided by UMTS. HSDPA currently supports downlink speeds of 1.8, 3.6, 7.2, and 14.4 Mbit/s. Long Term Evolution (LTE) is a promising standard for the next generation (4G) of mobile broadband networking.
Multiple-input and multiple-output (MIMO) requires the use of multiple antennas at both the transmitter and receiver. The signals from the antennas are combined to minimize errors and optimize data speed, providing better range and performance. However, the use of multiple inputs and outputs requires a device to utilize the same radio spectrum frequency. The United States presently uses the GSM-850 and GSM-1900 radio spectrum frequencies for cellular transmissions. GSM-850 uses 824-849 MHz for uplink and 869-894 MHz for downlink, providing channel numbers 128-251. GSM-1900 uses 1850-1910 MHz to uplink and 1930-1990 MHz to downlink, providing channel numbers 512-818. The MIMO concept defined in Third Generation Partnership Project Revision 7 (3GPP R7) and Revision 8 (MIMO R8), incorporated by reference herein in their entirety into this disclosure, requires the use of the same radio spectrum frequency for both transmission paths. These frequencies and antennas are used in spatial multiplexing or transmission diversity mode according to radio conditions. This allows for multiple simultaneous data streams, thereby increasing the data transmission rate.
MIMO R8 also requires twice the amount of antennas at both the transmitter and the receiver locations, even though the transmission takes place across a single frequency band. This creates interference in the signal, which decreases the actual gain in bandwidth created by MIMO R8. The additional signal used in MIMO R8 is another two-way transmit path. Although MIMO R8 can have up to four transmit paths, the uplink bandwidth is still equivalent to the downlink bandwidth, because each additional transmit path adds a duplex channel.
Demanding data services for individual users can exceed the capabilities of a single frequency carrier and/or radio path for a variety of transmission technologies. In this case, the capacity of multiple bi-directional frequency carriers and/or radio paths are combined, or “bonded” for the single demanding user. Multiple pre-existing bi-directional transmission pairs are allocated to the demanding user and traffic is spread across them. The Federal Communications Commission (FCC) recently auctioned the 700 MHz frequency spectrum. AWS-700 uses 776-794 MHz for uplink and 746-764 MHz for downlink.
As is, these transmission techniques offer useful means to boost individual peak throughput within the capabilities of the available transmission technology. However, bi-directional frequency carriers and/or radio paths, and the equipment required to use them, are best utilized if the data load and equipment capabilities are symmetrical. Unfortunately this is often not the case. Traffic for most data, audio, and video applications is heavily weighted in the downlink, server to user, direction. Roughly eight times as much data is downloaded to as is uploaded from mobile devices. The number of duplex signals available may limit these downlink requests. Many frequency bands are not intended for and not licensed for transmission by an individual user. Currently there are many of these frequencies available for downlink only which are being underutilized. Subscriber equipment, especially wireless, is also limited in terms of available space, power (battery life for mobile devices) and cost. The need for subscriber equipment to simultaneously transmit on all bonded frequency carriers and/or radio paths is therefore an unnecessary burden from an equipment complexity, cost and power perspective.
What is needed is a system that utilizes a downlink only channel to supplement the bandwidth of a conventional duplex channel to distribute the data load.